Additive blend for enhancing water vapor permeability and increasing cell size in thermoplastic foams

ABSTRACT

Polymeric foam and polymeric foam products that contain a foamable polymer material, at least one blowing agent, an additive blend of polyethylene oxide and a copolymer of polystyrene and maleic anhydride, and optionally, an infrared attenuating agent, are provided. In exemplary embodiments, the polyethylene oxide is ethoxylated polyethylene oxide. Additionally, in at least one embodiment, the blowing agent includes at least one hydrofluorocarbon blowing agent. The blend of ethoxylated polyethylene oxide and copolymer of polystyrene and maleic anhydride provides a water vapor permeability of 1.1 perm inch or greater in the extruded foam product and increases the average cell size of the foam product without detrimentally affecting physical or thermal properties of the product. Additionally, the additive acts as a cell enlarger, a water vapor permeability enhancer, a plasticizer, and a processing aid. A method of forming an extruded foam product is also provided.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates generally to extruded foam products, and more particularly, to a polystyrene foam containing a blend of ethoxylated polyethylene oxide and a styrene/maleic anhydride copolymer where the polymer foams have an improved water vapor permeability, have an enlarged average cell size, and possess no ozone depleting potential and a low global warming potential. A method of forming such polymer foams is also provided.

BACKGROUND OF THE INVENTION

Foamed resinous structures are useful in a wide variety of applications such as thermal insulation, in cushions, as packaging, and as adsorbents. Extruded foams are generally made by melting a polymer together with any desired additives to create a polymer melt. A blowing agent is mixed with the polymer melt at an appropriate temperature and pressure to produce a foamable gel mixture. The foamable gel mixture is then cooled and extruded into a zone of reduced pressure, which results in a foaming of the gel and the formation of the desired extruded foam product. As will be appreciated, the relative quantities of the polymer(s), blowing agent(s), and additives, as well as the temperature and manner in which the pressure is reduced will tend to affect the qualities and properties of the resulting foam product.

Traditional blowing agents used for extruded foam products include chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). One of the advantages of both CFC and HCFC blowing agents is their high solubility in a polymer melt during the manufacturing process. Higher blowing agent solubility promotes a reduction in viscosity when the blowing agent is mixed with the polymer melt. In turn, lower viscosity leads to lower energy requirements for mixing. On the other hand, a major disadvantage to these traditional blowing agents is that an increasing number of governments worldwide have mandated the elimination of CFC and HCFC blowing agents due to growing environmental concerns. CFCs, and many other halocarbons, have come to be recognized as serious global environmental threats due to their ability to cause stratospheric ozone depletion and global warming. The ozone depletion and global warming impact of chemicals such as CFCs and HCFCs are measured by the ozone depletion potential (ODP) and global warming potential (GWP) respectively.

In view of the mandatory phase out of blowing agents with a high ODP and a high GWP, there has been a movement to replace the conventional blowing agents with more environmentally friendly blowing agents, such as hydrofluorocarbons (HFCs) and CO₂, in insulating foam applications. Although HCFCs provide a superior thermal barrier compared to HFC and CO₂, the chlorine present in the HCFCs possesses an ozone depletion potential. Additionally, over time, the chlorofluorocarbon gas phase remaining in the foam is released into the atmosphere, thereby reducing the insulative value of the foam and potentially further contributing to ozone depletion and to the global warming potential. In addition, each of the “non-conventional” blowing agents leads to a different cell size and morphology, depending on the particular blowing agent chosen. Additionally, the cell sizes of the foams produced by these generally environmentally friendly blowing agents are too small to provide an acceptable insulative value to the foamed product and generally results in a higher density and a more costly product.

In addition, the water vapor permeability of the foams produced with HCFCs typically have a water vapor permeability of 1.0 perm inch or less. Desirably, the water vapor permeability of extruded foam boards is greater than 1.0 perm inch. Improving the water vapor permeability in extruded foam boards is becoming an important factor in building construction design and applications. The water vapor permeability of extruded foam boards is an important factor in inhibiting the potential for condensation as well as mold and fungal growth on the foamed boards and in the wall system in which the foam boards are used. When water, dust, and other microbial nutrients contaminate the foam board, they provide a support medium for the growth of bacteria, fungi, and/or mold in and on the foamed board. Bacterial, fungal, and mold growth may cause odor, discoloration, and/or product deterioration. Previous attempts to eliminate mold growth have been focused on limiting the intrusion of liquid water and the condensation of water vapor within the wall assembly.

Despite previous attempts to reduce the ODP and GWP, there remains a need in the art to achieve an extruded polymer foam that has an improved water vapor permeability and an increased cell size when non-HCFC blowing agents are used, that maintains the positive physical properties of conventional extruded polystyrene foams, that provides a foam product with increased insulation value (R-value), and that meets the stringent requirements for a reduction in the global warming potential and ozone depletion potential.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a composition for forming a closed cell, rigid thermoplastic polymer foam that includes a foamable polymer material, at least one blowing agent, an additive blend of polyethylene oxide and a styrene/maleic anhydride copolymer, and optionally, an infrared attenuating agent. The blowing agent may be selected from hydrofluorocarbons, C₁ to C₉ aliphatic hydrocarbons, C₁ to C₃ aliphatic alcohols, carbon dioxide, acetone, natural gases, air, water, ketones, ethers, methyl formate, hydrogen peroxide, and combinations thereof. The blend of polyethylene oxide and a styrene/maleic anhydride copolymer provides a water vapor permeability of 1.1 perm inch or greater to foamed products made utilizing the inventive composition. In exemplary embodiments, the foamable polymer material includes polystyrene, a blowing agent that includes an HFC blowing agent, and an infrared attenuating agent that includes graphite or nanographite. The polyethylene oxide and the copolymer of maleic anhydride and polystyrene have the chemical structures set forth in Formulas I and II:

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or other homologs, and

where m=100-2500 and n=100-2500. In at least one exemplary embodiment, the polyethylene oxide is an ethoxylated polyethylene oxide having Formula III

It is another object of the present invention to provide a foamed product that includes an extruded foamable composition comprising a foamable polymer material, at least one blowing agent, an additive blend of polyethylene oxide and a styrene/maleic anhydride copolymer, and optionally, one or more infrared attenuating agent. The polyethylene oxide and styrene/maleic anhydride copolymer have the chemical structures set forth in Formulas I and II above. In one or more exemplary embodiment, the polyethylene oxide is an ethoxylated polyethylene oxide having Formula III set forth above. The blend of polyethylene oxide and styrene/maleic anhydride copolymer increases the water vapor permeability and increases the average cell size of the foamed product without detrimentally affecting the physical or thermal properties of the foamed product. For example, a blend of polyethylene oxide (e.g., ethoxylated polyethylene oxide) and a styrene/maleic anhydride copolymer provides for a water vapor permeability of 1.1 perm inch or greater in the polymer foam product and provides a cell size from about 0.1 mm to about 0.2 mm in the polymer foam product. In exemplary embodiments, the foamable polymer material includes polystyrene, a blowing agent that includes an HFC blowing agent, and an infrared attenuating agent that includes nanographite.

It is a further object of the present invention to provide a method of forming a rigid, closed cell foam product that includes heating an alkenyl aromatic polymer material and an additive blend of polyethylene oxide and a copolymer of polystyrene and maleic anhydride, and optionally, an infrared attenuating agent, to a first temperature sufficient to melt the polymer material and form a polymer melt, incorporating at least one blowing agent into the polymer melt at a first pressure to form a foamable gel, cooling the foamable gel to a second temperature where the second temperature is less than the first temperature, and extruding the cooled polymer melt at a pressure sufficient to form a rigid, closed cell extruded foam product. The polyethylene oxide and styrene/maleic anhydride copolymer have the chemical structures set forth in Formulas I and II above, respectively. In one or more exemplary embodiment, the polyethylene oxide is an ethoxylated polyethylene oxide having Formula III set forth above. The method may also include compounding the blend of polyethylene oxide and styrene/maleic anhydride copolymer in a carrier, pelletizing the compounded blend of polyethylene oxide and styrene/maleic anhydride copolymer to form a pellet, and adding the pellet to the polymer melt.

It is an object of the present invention to provide a composition for forming a closed cell, rigid thermoplastic polymer foam that includes a styrene/maleic anhydride copolymer, polyethylene oxide, at least one blowing agent, and optionally, an infrared attenuating agent. In this exemplary embodiment, the styrene/maleic anhydride copolymer acts as the foamable polymer material. It is to be appreciated that in such embodiments, the foamable composition is free of added polystyrene and/or other (separate) foamable polymer materials. The styrene:maleic anhydride (S:MA) ratio may range from 70:30 (S:MA) to 99:1 (S:MA). The blowing agent may be selected from hydrofluorocarbons, C₁ to C₉ aliphatic hydrocarbons, C₁ to C₃ aliphatic alcohols, carbon dioxide, acetone, natural gases, air, water, ketones, ethers, methyl formate, hydrogen peroxide, and combinations thereof.

It is an advantage of the present invention that an additive blend of polyethylene oxide and a copolymer of polystyrene and maleic anhydride improves the water vapor permeability and increases the average cell size of the foamed product without detrimentally affecting the physical or thermal properties of the product.

It is another advantage of the present invention that the composition of the present invention has a low global warming potential and little or no ozone depleting potential.

It is yet another advantage of the present invention that the inclusion of the additive blend in the foamable composition requires no modification to existing manufacturing equipment and therefore no increase in manufacturing costs.

It is a further advantage of the present invention that the foams produced by the present composition have no toxicity to living creatures.

It is yet another advantage of the present invention that an additive blend of ethoxylated polyethylene oxide and a styrene/maleic anhydride copolymer provides a water vapor permeability greater than 1.1 perm inch to the extruded foam product.

It is an advantage of the present invention that an additive blend of ethoxylated polyethylene oxide and a styrene/maleic anhydride copolymer provides a cell size from about 0.10 mm to about 0.20 mm and an R-value/inch from about 5.0 to 7.0 in the extruded foam product.

The foregoing and other objects, features, and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description that follows. It is to be expressly understood, however, that the drawings are for illustrative purposes and are not to be construed as defining the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of this invention will be apparent upon consideration of the following detailed disclosure of the invention, especially when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of an extrusion apparatus for forming an extruded foam according to at least one exemplary embodiment of the invention;

FIG. 2 is a graphical illustration of the water vapor permeability (perm inch) vs. the percent of added blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride (actual percent);

FIG. 3 is a graphical illustration of the effect of the additive blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride on average cell sizes in an extruded polystyrene foam board;

FIG. 4 is a graphical illustration of the effect of the additive blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride on average cell sizes at 0.5 wt % graphite loading;

FIG. 5 is a graphical illustration of the effect of the additive blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride on extrusion pressure;

FIG. 6 is a graphical illustration of the effect of the additive blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride on mean cell sizes at 0.5 wt % graphite loading as measured by scanning electron microscopy;

FIG. 7 is scanning electron micrograph of a sample of an extruded polystyrene foam board containing 0.5 wt % graphite and 0.0 wt % of the additive blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride;

FIG. 8 is scanning electron micrograph of a sample of an extruded polystyrene foam board containing 1.0 wt % graphite and 0.0 wt % of the additive blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride;

FIG. 9 is scanning electron micrograph of a sample of an extruded polystyrene foam board containing 0.5 wt % graphite and 1.5 wt % of the additive blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride; and

FIG. 10 is scanning electron micrograph of a sample of an extruded polystyrene foam board containing 1.0 wt % graphite and 3.0 wt % of the additive blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. All references cited herein, including published or corresponding U.S. or foreign patent applications, issued U.S. or foreign patents, or any other references, are each incorporated by reference in their entireties, including all data, tables, figures, and text presented in the cited references. In the drawings, the thickness of the lines, layers, and regions may be exaggerated for clarity. It is to be noted that like numbers found throughout the figures denote like elements.

The terms “composition” and “inventive composition” may be used interchangeably herein. Additionally, the terms “foam board”, “extruded foam board”, and “inventive foam board” may be used interchangeably herein. Further, the terms “increased average cell size” and “enlarged average cell size” may be used interchangeably herein. Also, the phrase “copolymer of polystyrene and maleic anhydride” can be interchangeably used with “styrene/maleic anhydride copolymer”.

The present invention relates to polymer extruded or expanded foams that contain an additive blend of polyethylene oxide and a copolymer of polystyrene and maleic anhydride (“additive blend”) as both a water vapor permeability enhancing agent to increase the water vapor permeability of the foamed product and as a cell size enlarging agent to increase the average cell size of the foamed product. The additive blend of a polyethylene oxide and styrene/maleic anhydride copolymer increases the water vapor permeability and cell size of the foamed product without detrimentally affecting the physical or thermal properties of the product formed. The composition used to form extruded (or expanded) foams having an improved water vapor permeability and an increased cell size includes a foamable polymer material, at least one blowing agent (e.g., hydrofluorocarbon (HFC)), a blend of a polyethylene oxide and a styrene/maleic anhydride copolymer, and, in exemplary embodiments, an infrared attenuating agent (e.g., graphite or nanographite). The additive blend of a polyethylene oxide and styrene/maleic anhydride copolymer acts as a process aid and a plasticizer, enhances the solubility of the blowing agent, and lowers the die pressure.

The foamable polymer material is the backbone of the formulation and provides strength, flexibility, toughness, and durability to the final product. The foamable polymer material is not particularly limited, and generally, any polymer capable of being foamed may be used as the foamable polymer in the resin mixture. The foamable polymer material may be thermoplastic or thermoset. The particular polymer material may be selected to provide sufficient mechanical strength and/or to the process utilized to form final foamed polymer products. In addition, the foamable polymer material is preferably chemically stable, i.e., generally non-reactive, within the expected temperature range during formation and subsequent use in a polymeric foam. Non-limiting examples of suitable foamable polymer materials include alkenyl aromatic polymers, polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polyethylene, polypropylene, polycarbonates, polyisocyanurates, polyetherimides, polyamides, polyesters, polycarbonates, polymethylmethacrylate, polyphenylene oxide, polyurethanes, phenolics, polyolefins, styreneacrylonitrile (SAN), acrylonitrile butadiene styrene, acrylic/styrene/acrylonitrile block terpolymer (ASA), polysulfone, polyurethane, polyphenylenesulfide, acetal resins, polyamides, polyaramides, polyimides, polyacrylic acid esters, copolymers of ethylene and propylene, copolymers of styrene and butadiene, copolymers of vinylacetate and ethylene, rubber modified polymers, thermoplastic polymer blends, and combinations thereof.

In one exemplary embodiment, the foamable polymer material is an alkenyl aromatic polymer material. Suitable alkenyl aromatic polymer materials include alkenyl aromatic homopolymers and copolymers of alkenyl aromatic compounds and copolymerizable ethylenically unsaturated comonomers. In addition, the alkenyl aromatic polymer material may include minor proportions of non-alkenyl aromatic polymers. The alkenyl aromatic polymer material may be formed of one or more alkenyl aromatic homopolymers, one or more alkenyl aromatic copolymers, a blend of one or more of each of alkenyl aromatic homopolymers and copolymers, or blends thereof with a non-alkenyl aromatic polymer. Notwithstanding the components of the composition, the alkenyl aromatic polymer material may include greater than 50 or greater than 70 weight percent alkenyl aromatic monomeric units. In at least one embodiment of the invention, the alkenyl aromatic polymer material is formed entirely of alkenyl aromatic monomeric units.

Examples of alkenyl aromatic polymers include, but are not limited to, those alkenyl aromatic polymers derived from alkenyl aromatic compounds such as styrene, α-methylstyrene, ethylstyrene, vinyl benzene, vinyl toluene, chlorostyrene, and bromostyrene. In at least one embodiment, the alkenyl aromatic polymer is polystyrene.

Minor amounts of monoethylenically unsaturated compounds such as C₂ to C₆ alkyl acids and esters, ionomeric derivatives, and C₂ to C₆ dienes may be copolymerized with alkenyl aromatic compounds. Non-limiting examples of copolymerizable compounds include acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, acrylonitrile, maleic anhydride, methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, methyl methacrylate, vinyl acetate and butadiene.

The foamed products may be formed substantially of (e.g., greater than 95 percent), and in most embodiments, formed entirely of polystyrene. The foamable polymer material may be present in the composition in an amount from about 60% to about 95% by weight, in an amount from about 70% to about 90% by weight, or in an amount of about 85% to about 90% by weight. In exemplary embodiments, the foamable polymer material may be present in an amount from about 90% to about 95% by weight. As used herein, the term “% by weight” is meant to indicate a percentage based on 100% of the total weight of the dry components.

It is to be appreciated that the properties of the extruded foam or foam product may be modified by the selection of the molecular weight of the polymer. For example, the preparation of lower density extruded foam products is facilitated by using lower molecular weight polymers. On the other hand, the preparation of higher density extruded foam products is facilitated by the use of higher molecular weight polymers or higher viscosity resins.

The foamable composition may include at least one hydrofluorocarbon (HFC) blowing agent. The specific hydrofluorocarbon utilized is not particularly limited. A non-exhaustive list of examples of suitable blowing HFC blowing agents include 1,1-difluoroethane (HFC-152a), difluoroethane (HFC-152), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1-trifluoroethane (HFC-143a), difluoromethane (HFC-32), 1,3,3,3-pentafluoropropane (HFO-1234ze), pentafluoro-ethane (HFC-125), fluoroethane (HFC-161), 1,1,2,2,3,3-hexafluoropropane (HFC 236ca), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea), 1,1,1,3,3,3-hexafluoropropane (HFC-236fa), 1,1,1,2,2,3-hexafluoropropane (HFC-245ca), 1,1,2,3,3-pentafluoropropane (HFC-245ea), 1,1,1,2,3 pentafluoropropane (HFC-245eb), 1,1,1,3,3-pentafluoropropane (HFC-245fa), 1,1,1,4,4,4-hexafluorobutane (HFC-356mff), 1,1,1,3,3-pentafluorobutane (HFC-365mfc), FEA-1100 (DuPont), 2, 3,3,3-tetrafluoroprop-1-end (R-1234YF from Arkema), and combinations thereof.

Other blowing agents useful in the practice of this invention include inorganic blowing agents, organic blowing agents, and chemical blowing agents. Any suitable blowing agent may be used in the practice on this invention as a blowing agent. However, due to increased environmental concern over global warming and ozone depletion, in exemplary embodiments, the foamable composition is free of blowing agents containing chlorofluorocarbons (CFCs).

Non-limiting examples of organic blowing agents suitable for use in the present invention include C₂ to C₉ aliphatic hydrocarbons (e.g., methane, ethane, propane, n-butane, cyclopentane, isobutane, n-pentane, isopentane, and neopentane), C₁ to C₅ aliphatic and non-aliphatic alcohols (e.g., methanol, ethanol, n-propanol, isopropanol, and butanol). Natural gases such as carbon dioxide (CO₂), nitrogen (N₂), and/or argon (Ar) may also be used as a blowing agent. Water, air, ketones (e.g., acetone and methyl ethyl ketone), ethers (e.g., dimethyl ethers and diethyl ethers), methyl formate, acetone, and hydrogen peroxide may also be used as blowing agents. The blowing agents identified herein may be used singly or in combination. In exemplary embodiments, the blowing agent includes at least one hydrofluorocarbon (HFC) blowing agent. The blowing agent may be present in the composition in an amount from about 4.0% to about 10.0% by weight, and in exemplary embodiments, from about 4.0% to about 8.5% by weight, or from about 7.5% to about 8.0% by weight, or from about 7.6% to about 7.9% by weight. The blowing agent utilized in the inventive composition is selected such that the composition has zero ozone depletion and low to no global warming potential. In at least one exemplary embodiment, the blowing agent is 1,1-difluoroethane (HFC-152a), 1,1,1,2-tetrafluoroethane (HFC-134a), or a combination of 1,1-difluoroethane (HFC-152a) and 1,1,1,2-tetrafluoroethane (HFC-134a).

As discussed above, the composition may also contain at least one infrared attenuating agent to increase the R-value of the foam product. Hydrofluorocarbon blowing agents, while environmentally friendly, tend to decrease the R-value of the foam product compared to a conventional HCFC foamed product (e.g., R-value per inch of 5.0) at comparable densities. As taught in U.S. Patent Publication Number 2008/0242752 to Delaviz, et al., which is incorporated herein by reference in its entirety, it was discovered that the addition of low levels of an infrared attenuating agent to a foamable composition containing a hydrofluorocarbon blowing agent increased the R-value of the foam to an amount comparable to, or better than, a foam produced with an HCFC blowing agent (e.g., 1-chloro-1,1-difluoroethane (HCFC-142b)).

It was also discovered that, generally, foams produced with an infrared attenuating agent and a hydrofluorocarbon blowing agent had an R-value per inch of 5.0 or greater. Non-limiting examples of suitable infrared attenuating agents for use in the present composition include graphite, nanographite, carbon black, powdered amorphous carbon, asphalt, granulated asphalt, milled glass, fiber glass strands, mica, black iron oxide, metal flakes (e.g., aluminum flakes), carbon nanotube, nanographene platelets, carbon nanotubes (both single and multi-walled), carbon nanofiber, activated carbon, metal oxides (e.g., titanium dioxide, aluminum oxide, etc.), and combinations thereof. As used in conjunction with this invention, “nano” compounds, such as, for example, “nanographite”, are intended to denote compounds that have a thickness in at least one dimension, most likely the thickness of the particle, of less than about 100 nanometers. In exemplary embodiments, the infrared attenuating agent is present in the foam composition in an amount from about 0% to about 5.0% by weight of the total dry components of the composition. In other embodiments, the infrared attenuating agent may be present in an amount from about 0.01% to about 5.0% by weight, from about 0.05% to about 1.0% by weight, or in an amount of about 0.1% to about 0.5% by weight.

Although the infrared attenuating agent increases the R-value for foams that include hydrofluorocarbon blowing agents, the addition of infrared attenuating agents also tends to decrease the cell size of the cells in the foam, which results in undesirable final foamed products. In particular, small cell sizes tend to increase board bulk density, increase product cost, and reduce the process window during the extrusion process. Further, infrared attenuating agents undesirably increase the melt rheology, which will result in an increase of the die pressure.

In addition, although the use of non-CFC blowing agents reduces or eliminates ozone depletion and non-CFC blowing agents have a low to no global warming potential, they do not provide a significant improvement in the water vapor permeability over conventional CFC blowing agents. As used herein, “water vapor permeability” is meant to denote the ability of moisture (e.g., water vapor) to pass through the foam board. Having proper or adequate water vapor permeability reduces or eliminates the potential for condensation and/or mold and fungal growth on the foamed boards and/or in the wall system in which the foam boards are used. As is known in the art, mold and fungal growth may cause undesirable odor, discoloration, and/or product deterioration. A higher water vapor permeability enhances the performance of the foam board, thereby allowing water vapor to migrate through the board (and thus the building wall), minimizing or eliminating the occurrence of condensation and mold/fungal growth.

Closed cell extruded foam boards formed using CFC blowing agents, such as HCFC-142b, typically have a water vapor permeability of 1.0 perm inch or less. It has been determined that foam boards produced with HFC blowing agents, such as HFC-134a and/or HFC-152a, and/or CO₂ do not have a significant impact on improving the water vapor permeability of foam board, as these boards also typically have a water vapor permeability of less than about 1.0 perm inch. To improve the water vapor permeability of foamed boards formed with non-CFC blowing agents and/or to compensate for the decreased cell size caused by the infrared attenuating agent and the blowing agent (e.g., HFC-134a and/or HFC-152a and/or CO₂), a blend of (1) a polyethylene oxide and (2) a copolymer of maleic anhydride and polystyrene having the chemical structures set forth in Formulas I and II may be included in the foamable composition:

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or other homologs, and

where m=100-2500 and n=100-2500. It is to be appreciated that foams produced utilizing the inventive composition containing the additive blend can be used in markets that desire improved water vapor permeability and/or in markets that desire increased cell size.

As noted above, the polyethylene oxide can be end-capped with alkoxy groups such as methoxy, ethoxy, propyloxy, butoxy, as well as other homologs compounds. Although any of these homologs of polyethylene oxide are suitable for use in the inventive composition, reference will be made herein to ethoxylated polyethylene oxide, which has the formula set forth in Formula III

where n=5-50.

It has been surprisingly discovered that the addition of the additive blend of ethoxylated polyethylene oxide and a copolymer of maleic anhydride and polystyrene in an amount of as little as 1.0% by weight produces a foam board having a water vapor permeability that is greater than 1.1 perm inch. Additionally, it has been discovered that the addition of as low as 1.0% by weight of a blend of ethoxylated polyethylene oxide and a styrene/maleic anhydride copolymer in the foamable composition results in an enhancement of the water vapor permeability by more than 50%. The addition of the polystyrene/polyethylene oxide copolymer to the foamable composition provides a water vapor permeability of greater than 1.1 perm inch, and in exemplary embodiments, from 1.1 perm inch to 1.5 perm inch, from 1.2 perm inch to 1.5 perm inch, or from 1.3 perm inch to 1.5 perm inch without an adverse and/or negative impact on the general physical and thermal properties of the extruded foam board.

It has also been surprisingly discovered that the additive blend of ethoxylated polyethylene oxide and a copolymer of maleic anhydride and polystyrene increases the cell size of the polymer foam and offsets or even negates the decreased cell size caused by the HFC blowing agent and/or the infrared attenuating agents. In addition, the blend of ethoxylated polyethylene oxide and a copolymer of maleic anhydride and polystyrene has a positive affect on the processability of the HFC blowing agent(s) in the composition by both widening the process window and enhancing the HFC solubility in the polymer melt. Thus, the additive blend of ethoxylated polyethylene oxide and a styrene/maleic anhydride copolymer present in the inventive composition acts as a cell enlarger, a plasticizer, and a processing aid. Further, the polyethylene oxide moieties add polarity to the polymer melt and help to improve the solubility of HFC blowing agents (e.g., HFC-134a, HFC-152a, and CO₂). Due to the plasticizing effect of the blend of ethoxylated polyethylene oxide and a copolymer of maleic anhydride and polystyrene, free volume is created in the melt, which results in higher blowing agent solubility and a lowering of the melt viscosity.

The use of the blend of ethoxylated polyethylene oxide and a styrene/maleic anhydride copolymer in conjunction with the infrared attenuating agent permits the formation of a foam with an optimized cell size and a high insulation value (R-value) and to optimize the physical properties of the final foamed product. In addition, the blend of ethoxylated polyethylene oxide and a copolymer of maleic anhydride and polystyrene provides an increased cell size to the foamed product without detracting from the physical and thermal properties the foam. It is believed that the blowing agent(s) and the infrared attenuating agent(s) have a synergistic affect on the cell morphology and decrease in cell size that is surprisingly overcome by the addition of the blend of ethoxylated polyethylene oxide and a copolymer of maleic anhydride and polystyrene.

In addition, the inclusion of an infrared attenuating agent in the foamable composition has no significant impact on the improvement of the water vapor permeability of the extruded foam boards caused by the additive blend of ethoxylated polyethylene oxide and a styrene/maleic anhydride copolymer. Thus, foams produced with an infrared attenuating agent, a hydrofluorocarbon blowing agent, and the blend of ethoxylated polyethylene oxide and a copolymer of maleic anhydride and polystyrene have both an increased R-value per inch and an increased water vapor permeability.

The blend of ethoxylated polyethylene oxide and a styrene/maleic anhydride copolymer may be added to the composition in an amount from about 0.5% to about 5.0% by weight, particularly from about 1.0% to about 4.0% by weight, and in exemplary embodiments, from about from 1.0% to about 3.0% by weight of the total dry components of the composition.

Further, the inventive composition may contain a fire retarding agent in an amount up to about 1.0% by weight. For example, fire retardant chemicals may be added in the extruded foam manufacturing process to impart fire retardant characteristics to the extruded foam products. In exemplary embodiments, the fire retarding agent is added to the foamable gel, which is described below with respect to the formation of the inventive foam. Non-limiting examples of suitable fire retardant chemicals for use in the inventive composition include brominated aliphatic compounds such as hexabromocyclododecane and pentabromocyclohexane, brominated phenyl ethers, esters of tetrabromophthalic acid, and combinations thereof.

Optional additives such as nucleating agents, plasticizing agents, pigments, elastomers, extrusion aids, antioxidants, fillers, antistatic agents, biocides, and/or UV absorbers may be incorporated into the inventive composition. These optional additives may be included in amounts necessary to obtain desired characteristics of the foamable gel or resultant extruded foam products. The additives may be added to the polymer mixture or they may be incorporated in the polymer mixture before, during, or after the polymerization process used to make the polymer.

In one exemplary embodiment, the foamable polymer material is omitted from the composition and the styrene/maleic anhydride copolymer from the additive blend acts as the foamable polymer material. In this instance, the styrene:maleic anhydride (S:MA) ratio may range from 70:30 (S:MA) to 99:1 (S:MA), or from 70:30 to 95:5 (S:MA). It is to be appreciated that in such embodiments, the foamable composition is free of additional polystyrene and/or other (separate) foamable polymer materials. The remainder of the inventive composition remains the same as that described in detail above, and includes the polyethylene oxide present in the additive blend as the cell size enhancer and water vapor permeability enhancer, one or more blowing agents, and optionally, infrared attenuating agent(s), flame retardant(s), and/or other additives.

To form an extruded polymer foam according to the principles of the instant invention, the foamable polymer material (e.g., polystyrene) may be heated to a temperature at or above the polymer's glass transition temperature or melting point to form a plasticized or a melt polymer material. The infrared attenuating agent (e.g., nanographite) may be blended in the polymer melt or dry blended with the polymer material/carrier prior to plasticizing or melting the foamable polymer material. It is to be appreciated that nanographite may also be added directly as a powder, in a compact form, or in a slurry. The blend of ethoxylated polyethylene oxide and copolymer of polystyrene and maleic anhydride may be compounded in a carrier such as polystyrene, pelletized, and added to the polymer melt, such as is demonstrated in the examples below. Alternatively, the additive blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer may be added directly, may use other carriers/polymers, or may be dissolved in a solvent such as alcohol and added to the extrusion as a liquid using a pump.

It is noted that in an embodiment where the styrene maleic anhydride copolymer is utilized as the foamable polymer material, the procedure for forming the polymer melt is the same as set forth above with the exception that the styrene maleic anhydride copolymer is substituted for the polystyrene and the additive blend consists of the polyethylene oxide.

One or more blowing agents (e.g., 1,1-difluoroethane (HFC-152a) and/or 1,1,1,2-tetrafluoroethane (HFC-134a)) is incorporated or mixed into the melt polymer material by any conventional method known to those of skill in the art such as, for example, with an extruder, a mixer, or a blender. As the blowing agent is added to the polymer melt, the blowing agent becomes soluble, i.e. dissolves, in the polymer melt and forms a foamable gel. Additionally, the blowing agent may be mixed with the melt polymer material at an elevated pressure sufficient to prevent substantial expansion of the melt polymer material and to generally disperse the blowing agent(s) substantially homogeneously or heterogeneously in the melt polymer material.

The foamable gel may then be cooled to a die melt temperature. The die melt temperature is typically cooler than the melt mix temperature to optimize the physical characteristics of the foamed product. In addition, that the die pressure may be sufficient to prevent, or at least minimize, pre-foaming of the foamable gel. Pre-foaming is the undesirable premature foaming of the foamable gel before extrusion of the gel into a region of reduced pressure. Thus, the die pressure varies depending upon the identity and amount of blowing agent(s) present in the foamable gel. The foamable gel may then be extruded through a die having a desired shape to a zone of lower or reduced pressure to form the desired foamed structure or foamed product. The zone of lower pressure is at a pressure lower than that in which the foamable gel is maintained prior to extrusion through the die. The lower pressure may be superatmospheric or subatmospheric (i.e., a vacuum), but in most embodiments, it is at atmospheric level. The foam thus produced is a rigid, closed cell, polymer foam.

A screw extruder for use in the present invention is generally indicated at reference numeral 10 in FIG. 1. The screw extruder for use in the instant invention may equally be a single screw or twin screw extruder. Reference is made herein with respect to a single screw extruder. The extruder 10 is formed of a barrel 12 and at least one screw 14 that extends substantially along the length of the barrel 12. A motor (M) may be used to power the screw 14. The screw 14 contains helical flights 16 rotating in the direction of arrow 18. The flights 16 of the screw 14 cooperate with the cylindrical inner surface of the barrel 12 to define a passage for the advancement of the resin and reinforcement fibers through the barrel 12. The foamable polymer material may be fed into the screw extruder 10 as flowable solid, such as beads, granules, or pellets from one or more feed hoppers 20.

As the foamable polymer material flows through the extruder 10 in the direction of arrow 18, the spacing between the flights 16 of the screw 14 decreases. Thus, the volume between the flights 16 decreases as the polymer melts flows downstream. The term “downstream” as used herein refers to the direction of resin and fiber flow through the barrel 12. This decreasing volume, together with the mechanical action and friction generated from the barrel 12 and the screw 14, causes the foamable polymer material to melt and form the melt polymer material.

It is to be appreciated that the flights 16 of the screw 14 cooperate with the cylindrical inner surface of the barrel 12 to define a passage for the advancement of the polymer melt through the barrel 12. As shown in FIG. 1, ports are provided at designated positions on the extruder for the insertion of the infrared attenuating agent, the blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride, and for the injection of the blowing agent(s). Specifically, a hopper 22 is provided downstream of the feed hopper 20 to feed the infrared attenuating agent into the barrel 12. The infrared attenuating agent and the additive blend of ethoxylated polyethylene oxide and a styrene/maleic anhydride copolymer are mixed into the polymer melt by the rotation of the screw 14. It is to be noted, however, that other ports and/or hoppers may be present on the barrel 12 for the inclusion of other materials or additives, such as, but not limited to, flame retardants, nucleating agents (e.g., talc), biocides, plasticizing agents, pigments, elastomers, extrusion aids, antioxidants, fillers, and/or antistatic agents.

In at least one embodiment, the resin and the blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride are substantially simultaneously fed into the barrel 12 of the extruder 10 through feed hopper 22. As used herein, the term “substantially simultaneously fed” is meant to indicate that the polymer resin and the blend of ethoxylated polyethylene oxide and a copolymer of polystyrene and maleic anhydride are fed into the barrel 12 at the same time or at nearly the same time.

Once the infrared attenuating agent, blowing agent(s), and the additive blend of ethoxylated polyethylene oxide and a styrene/maleic anhydride copolymer have been introduced into the barrel 12, the resulting foamable mixture is subjected to additional blending to substantially uniformly distribute the infrared attenuating agent, blowing agent, and the blend of ethoxylated polyethylene oxide and a styrene/maleic anhydride copolymer throughout the foamable mixture.

The heat from the internal friction from the screw 14 within the barrel 12 causes the blowing agent to be uniformly or substantially uniformly dispersed for improved solubility. The foamable mixture is subsequently cooled to a lower temperature in a melt cooler 25 and then conveyed from the extruder 10 through an extrusion die 26 which is designed to shape the foam into a desired shape and to create a pressure drop which permits the blowing agent to expand and develop a foamed cell structure in the form of a foam layer or slab. In particular, the foamable mixture enters an area of reduced pressure as it exits the die. The polymeric foam may be subjected to additional processing such as calendaring, water immersion, cooling sprays, post-steaming, or other operations to control the thickness and other properties of the resulting foam product.

The foam composition produces rigid, closed cell, polymer foam boards prepared by an extruding process. Extruded foams have a cellular structure with cells defined by cell membranes and struts. Struts are formed at the intersection of the cell membranes, with the cell membranes covering interconnecting cellular windows between the struts. In the present invention, the inventive composition produces substantially closed cellular foams with an average density of about 1.3 lbs/ft³ to about 3.0 lbs/ft³, from about 1.5 lbs/ft³ to about 4.0 lbs/ft³, or from about 1.3 lbs/ft³ to about 4.0 lbs/ft³. It is to be appreciated that the phrase “substantially closed cell” is meant to indicate that the foam contains all closed cells or nearly all of the cells in the cellular structure are closed. In most exemplary embodiments, not more than about 5.0% of the cells are open cells. The closed cell structure helps to increase the R-value of a formed, foamed insulation product. It is to be appreciated, however, that it is within the purview of the present invention to produce an open cell structure, although such an open cell structure is not an exemplary embodiment.

Additionally, the inventive foam composition produces extruded foams that have insulation values (R-values) that are equal to or better than conventional extruded foams produced with 1-chloro-1,1-difluoroethane (HCFC-142b). The R-value per inch of the inventive foams and foam products may be from 5.0 to 7.0. In at least one embodiment, the R-value per inch is from 5.0 to 6.0. In addition, the average cell size of the inventive foam and foamed products is about 0.1 mm to about 0.2 mm, or from about 0.14 mm to about 0.16 mm. In some embodiments, the average cell size is from about 0.12 mm to about 0.16 mm. The extruded inventive foam may be formed into an insulation product such as rigid insulation boards, insulation foam, packaging products, and building insulation or underground insulation (e.g., highway, airport runway, railway, and underground utility insulation).

Another aspect of the extruded inventive foams is that they possess a high level of dimensional stability. For example, the change in dimension in any direction is about 5% or less. In addition, the foam formed by the inventive composition is desirably monomodal and the cells have a relatively uniform average cell size. As used herein, the average cell size is an average of the cell sizes as determined in the X, Y and Z directions. In particular, the “X” direction is the direction of extrusion, the “Y” direction is the cross machine direction, and the “Z” direction is the thickness. In the present invention, the highest impact in cell enlargement is in the X and Y directions, which is desirable from an orientation and R-value perspective. In addition, further process modifications would permit increasing the Z-orientation to improve mechanical properties while still achieving an acceptable thermal property. The extruded inventive foam can be used to make insulation products such as rigid insulation boards, insulation foam, and packaging products.

There are numerous advantages of utilizing the composition of the present invention to form foam products. For example, the blowing agent utilized in the inventive formulation has a lower global warming potential than current HFC-142b and has zero ozone depleting potential. In addition, the infrared attenuating agent and the additive blend of ethoxylated polyethylene oxide and copolymer of polystyrene and maleic anhydride may be added to the melt polymer in a conventional fashion. Therefore, in at least some exemplary embodiments, there is no need to modify existing equipment or change the manufacturing lines to accommodate either the infrared attenuating agent or the blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer. In addition, the blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer is environmentally friendly and does not create any negative environmental concerns. Further, the blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer increases the water vapor permeability and increases the average cell size of the foamed product without detrimentally affecting the physical or thermal properties of the product. Additionally, the addition of the blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer improves the overall surface quality of the foam.

Additionally, the blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer improves the solubility of the HFC blowing agent(s) in the foamable composition. The blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer acts as a plasticizer to reduce the melt viscosity and lower the extrusion pressures. Also, the presence of maleic anhydride as well as polyethylene oxide moieties provides polarity through the C—CO—C and C—O—C bonds in the matrix, resulting in an improved solubility of blowing agents such as HFC-134a, HFC-152a, and CO₂. Additionally, through the plasticization, the polyethylene oxide moieties create free volume in the matrix, which results in higher blowing agent solubility and a lowered melt viscosity. Overall, the blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer acts as process aid and, as is demonstrated in the following examples, lowers the extrusion pressure.

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples illustrated below which are provided for purposes of illustration only and are not intended to be all inclusive or limiting unless otherwise specified.

Examples Water Vapor Permeability

Compositions containing polystyrene, a mixture of HFC-134a/HFC-152a as blowing agents, graphite, and a blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer (Additive Blend) as depicted in Table 1 were formed and used to generate foam board samples. In particular, nanographite was compounded at 20% active in general purpose polystyrene with the following characterics; Mw 253000, Mn 61300, Mz 532500, Mw/Mn (polydispersity) 3.44. The Additive Blend was compounded in general purpose polystyrene at 0.5%, 1/0%, 1.5%, 2.0%, 4%, 6%, 8%, 10%, and 12% active. The blowing agent utilized was a 50:50 blend of HFC-134a/HFC-152a at 7.5 wt % based on the resin weight. Foam boards were formed from the composition on an Owens Corning horizontal pilot line extrider at a 160 kg/hour dry throughput rate.

TABLE 1 Water Additive Vapor Blowing Additive Blend Blend Graphite Graphite Flame Perm Agent (Compounded) (Actual) (Compounded) (Actual) Retardant (Perm Sample (%) (%) (%) (%) (%) (%) Inch) 1 7.5 0.0 0.0 2.5 0.5 1.0 1.021 2 7.5 0.5 0.13 2.5 0.5 1.0 0.975 3 7.5 1.0 0.25 2.5 0.5 1.0 0.975 4 7.5 1.5 0.38 2.5 0.5 1.0 0.988 5 7.5 2.0 0.50 2.5 0.5 1.0 1.011 6 7.5 4.0 1.00 2.5 0.5 1.0 1.497 7 7.5 6.0 1.50 2.5 0.5 1.0 1.431 8 7.5 8.0 2.00 2.5 0.5 1.0 1.428 9 7.5 10.0 2.50 2.5 0.5 1.0 1.481 10 7.5 12.0 3.00 2.5 0.5 1.0 1.447

Once the foam boards were made, the water vapor permeability of the boards were tested according to the procedure set forth in ASTM E-96 (Standard Test Method For Water Vapor Transmission Of Materials (Dessicant Method)). The test method involves filling a non-permeable test dish with desiccant to within ¼ inch of the specimen. The perimeter of the dish is sealed to prevent vapor diffusion either into or out of the dish. The dish containing the specimen and the desiccant is then placed in a temperature and humidity controlled room and weighed periodically until a steady state weight gain is achieved. The water vapor permeability is then calculated from the obtained data. The results are depicted in FIG. 2.

As shown in FIG. 2, the addition of the blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer in amounts as low as 1.0% caused a significant increase in the water vapor permeability of the foamed boards. Amounts from about 1.0% to about 3.0% of the blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer had a significant improvement in water vapor permeability. It was also noted that there was no significant increase in the water vapor permeability as additional ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer was added to the polymer mix over about 3%.

Inclusion of a Blend of Ethoxylated Polyethylene Oxide and Styrene/Maleic Anhydride Copolymer in an Extruded Polystyrene Foam Board

Compositions containing polystyrene, a mixture of HFC-134a/HFC-152a as blowing agents, graphite, and a blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer (Additive Blend) as depicted in Table 2 were formed and used to generate foam board samples. In particular, nanographite was compounded at 20% active in general purpose polystyrene with the following characterics; Mw 201800, Mn 53900, Mz 407600, Mw/Mn (polydispersity) 3.4 and melt flow index of 10.7 (as determined using ASTM D1238 condition G). The blend of ethoxylated polyethylene oxide and styrene/maleic anhydride copolymer was compounded in general purpose polystyrene at 25% active. The blowing agent utilized was a 50:50 blend of HFC-134a/HFC-152a at 7.0 wt % based on the resin weight. Foam boards were formed from the composition on an Owens Corning hydrovac horizontal pilot line extrusion at a 160 kg/hour throughput rate.

TABLE 2 Graphite Additive Blend (20%) (25%) Ave. % added/ % added/ Density X-cell Y-cell Z-cell Cell Orientation Sample actual % actual % (pcf) (mm) (mm) (mm) (mm) X:Z Control 1 2.5/0.5  0/0 1.77 0.110 0.120 0.120 0.117 0.92:1 1 2.5/0.5 4.00/1.0 1.68 0.120 0.110 0.120 0.120 0.94:1 2 2.5/0.5  6.0/1.5 1.63 0.127 0.136 0.140 0.134 0.91:1 3 2.5/0.5 12.0/3.0 1.93 0.142 0.149 0.146 0.148 0.97:1 4 2.5/0.5 12.0/3.0 1.62 0.153 0.170 0.161 0.161 0.96:1

The following was noted and/or concluded from Table 2:

-   -   Control 1 had 0.5% actual graphite in the foamable composition.         In addition, Control 1 did not contain any Additive Blend. The         average cell size for Control 1 was 0.117 mm.     -   Samples 1, 2, 3, and 4 contained the same graphite loading and         increasing levels of the Additive Blend as a cell enlarger. When         3.0% actual Additive Blend was added as shown in Samples 3 and         4, the average cell increased to 0.146 mm and 0.161 mm         respectively. It was determined that this was an approximately         38% increase in the average cell size (over the control) when         3.0% Additive Blend is added. It was noted that Sample 3 had a         much higher density (i.e., 1.93 pcf), and it is believed that         this higher density explains why the average cell for Sample 3         was 0.148 mm, and not closer to 0.161 mm as in Example 4.     -   Sample 1, which contained a 1.0% Additive Blend, had essentially         no effect on the average cell size over the Control sample. It         was noted that Sample 1 was much closer in density to Sample 4         and it was therefore believed to explain why higher levels of         the Additive Blend in the foamable composition acted as a cell         enlarger at comparable densities.     -   There is a larger effect of the Additive Blend on the average         cell sizes in the presence of 0.5 wt % graphite, as is         graphically illustrated in FIGS. 3 and 4.

TABLE 3 Additive Static Graphite (20%) Blend (25%) Extrusion Mix Die % added/ % added/ Out Out Pressure Sample actual % actual % (bars) (bars) (bars) Control 2 5.0/1.0 0/0 232.6 163.2 61.00 1 5.0/1.0 2.0/0.5 216.7 157.7 64.17 2 5.0/1.0 4.0/1.0 213.8 155.3 67.02 3 5.0/1.0 6.0/1.5 202.3 150.8 67.34

The following was noted and/or concluded from Table 3:

-   -   Comparing the Control having 0% PEO additive with Sample 3         having 1.5% of the Additive Blend, it can be seen that there is         13% and 8% reduction in extrusion and static mixture pressures,         respectively. The effect of the Additive Blend on extrusion         pressure was more pronounced in the presence of 1.0 wt %         graphite as shown in Table 3 and illustrated in FIG. 5. The         extrusion pressure was 232.6 and 202.30 bars at the 0.0 and 1.5         wt % the Additive Blend, respectively. The overall lower         extrusion pressure equated to better processability and a wider         process window. It was concluded that the plasticization effect,         polarity, and hydrophilicity of the Additive Blend enhanced the         HFC-134a and HFC-152a solubility in the polystyrene melt,         lowered viscosity, and reduced the overall pressures of the         extrusion process.     -   It was noted that there were not any adverse and/or negative         impact on the general physical and thermal properties of the         extruded foam board when the Additive Blend was used in the         foamable composition.

Scanning Electron Microscopy (SEM)

The cell morphology of the foam board formed above was also studied using scanning electron microscopy (SEM). This methodology (i.e., the SEM) shoes the impact of the Additive Blend on the average cell sizes is depicted both in Table 4 and in FIG. 6. The average cell sizes were 0.113 mm and 0.203 mm in the presence of 0.0 and 3.0 wt % of the Additive Blend, respectfully. This was calculated to be an approximate 80% increase in cell size.

TABLE 4 Mean Cell Sizes Measured By SEM Graphite Additive Blend Mean Cell Sample Wt % actual Wt % actual Sizes mm Control 1 0.5 0 0.113 Sample 2 0.5 1.5 0.180 Sample 4 0.5 3.0 0.203

The SEM analysis of the extruded boards showed that as the cells become larger, the cell wall thickness and strut diameter generally become smaller, as is shown in Table 7.

TABLE 5 Cell Wall Additive Total Struts Graphite Blend Cell Cell Ave. Total Ave. Wt % Wt % Cells/ Wall/ Walls Std. Struts/ Struts Std. Sample actual actual mm² mm Counted Dev. mm² Counted Dev. Control 1 0.5 0 113 12 24 0.9/0.41 170 170 3.5/1.02 Sample 1 1.0 1.0 112 12.5 25 0.6/0.21 172 172 2.6/0.63 Sample 2 0.5 1.5 71 8.0 16 1.0/0.35 106 106 4.7/0.92 Sample 4 0.5 3.0 61 8.0 16 1.4/0.74 106 106 5.3/2.05

The impact of the Additive Blend on cell morphology in the presence of 0.5 and 1.0 wt % graphite is depicted in the SEM micrographs depicted in FIGS. 7-10.

The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. The invention is not otherwise limited, except for the recitation of the claims set forth below. 

1. A composition for forming a closed cell, rigid thermoplastic polymer foam comprising: a foamable polymer material; at least one blowing agent; and an additive blend including polyethylene oxide having the formula

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or other homologs and a styrene maleic anhydride copolymer having the formula

where m=100-2500 and n=100-2500.
 2. The composition of claim 1, wherein said polyethylene oxide is an ethoxylated polyethylene oxide having the formula

where n=5-50.
 3. The composition of claim 1, further comprising at least one infrared attenuating agent.
 4. The composition of claim 3, wherein said one or more infrared attenuating agent is selected from nanographite, carbon black, powdered amorphous carbon, activated carbon, asphalt, granulated asphalt, milled glass, fiber glass strands, mica, black iron oxide, metal flakes, metal oxides, carbon nanotube, nanographene platelets, carbon nanofiber, activated carbon, titanium dioxide and combinations thereof.
 5. The composition of claim 1, wherein said at least blowing agent is selected from hydrofluorocarbons, C₁ to C₉ aliphatic hydrocarbons, C₁ to C₃ aliphatic alcohols, carbon dioxide, acetone, natural gases, air, water, ketones, ethers, methyl formate, hydrogen peroxide and combinations thereof.
 6. The composition of claim 1, wherein said additive blend enhances the solubility of hydrofluorocarbon blowing agents in a polymer melt.
 7. The composition of claim 3, wherein: said foamable polymer material is present in said composition in an amount from about 60% to about 95% by weight of the total dry components of the composition; said at least one blowing agent is present in said composition in an amount from about 4.0% to about 10.0% by weight of the total dry components of the composition; said additive blend is present in said composition in an amount from about 0.5% to about 5.0% by weight of the total dry components of the composition; and said infrared attenuating agent is present in said composition in an amount from about 0.01% to about 5.0% by weight of the total dry components of the composition.
 8. A rigid thermoplastic polymer foam product comprising: an extruded foamable composition, said foamable composition including: a foamable polymer material; at least one blowing agent; and an additive blend including polyethylene oxide having the formula (I)

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or other homologs and a styrene maleic anhydride copolymer having the formula (II)

where m=100-2500 and n=100-2500.
 9. The thermoplastic polymer foam product of claim 8, wherein said polyethylene oxide is an ethoxylated polyethylene oxide having the formula (III)

where n=5-50.
 10. The thermoplastic polymer foam product of claim 8, wherein said at least blowing agent is selected from hydrofluorocarbons, C₁ to C₉ aliphatic hydrocarbons, C₁ to C₃ aliphatic alcohols, carbon dioxide, acetone, natural gases, air, water, ketones, ethers, methyl formate, hydrogen peroxide and combinations thereof.
 11. The thermoplastic polymer foam product of claim 8, further comprising an infrared attenuating agent selected from nanographite, carbon black, activated carbon, powdered amorphous carbon, asphalt, granulated asphalt, milled glass, fiber glass strands, mica, black iron oxide, metal flakes, metal oxides, carbon nanotube, nanographene platelets, carbon nanofiber, activated carbon, titanium dioxide and combinations thereof.
 12. The thermoplastic polymer foam product of claim 11, wherein said additive blend increases the average cell size of said foam product including said infrared attenuating agent compared to foam products formed without said additive blend and including said infrared attenuating agent.
 13. The thermoplastic polymer foam product of claim 8, wherein said additive blend increases the water vapor permeability of said foamed product without detrimentally affecting the physical or thermal properties of said foamed product.
 14. The thermoplastic polymer foam product of claim 13, wherein said additive blend enhances the solubility of hydrofluorocarbon blowing agents in a polymer melt.
 15. The thermoplastic polymer foam product of claim 8, wherein said additive blend provides a cell size from about 0.1 mm to about 0.2 mm in said polymer foam product.
 16. A method of forming a rigid, closed cell foam product comprising: heating at least one alkenyl aromatic polymer material and an additive blend including polyethylene oxide having the formula

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or other homologs and a styrene maleic anhydride copolymer having the formula

where m=100-2500 and n=100-2500 to a first temperature sufficient to melt said at least one polymer material and form a polymer melt; incorporating one or more blowing agents into said polymer melt at a first pressure to form a foamable gel; cooling said foamable gel to a second temperature, said second temperature being less than said first temperature; and extruding said cooled polymer melt at a pressure sufficient to form a rigid, closed cell extruded foam product having a water vapor permeability of at least 1.1 perm inch.
 17. The method of claim 16, wherein said polyethylene oxide is an ethoxylated polyethylene oxide having the formula

where n=5-50.
 18. The method of claim 16, wherein said at least blowing agent is selected from hydrofluorocarbons, C₁ to C₉ aliphatic hydrocarbons, C₁ to C₃ aliphatic alcohols, carbon dioxide, acetone, natural gases, air, water, ketones, ethers, methyl formate, hydrogen peroxide and combinations thereof.
 19. The method of claim 16, wherein said heating step further comprises heating an infrared attenuating agent to incorporate said infrared attenuating agent into said polymer melt.
 20. The method of claim 16, wherein said additive blend and said at least one processing aid are simultaneously or substantially simultaneously added to said polymer melt.
 21. The method of claim 16, further comprising: compounding said additive blend in a carrier; pelletizing said compounded additive blend to form a pellet; and adding said pellet to said polymer melt.
 22. A composition for forming a closed cell, rigid thermoplastic polymer foam comprising: a styrene maleic anhydride copolymer having the formula

where m=100-2500 and n=100-2500; a cell size and water permeable enhancing agent consisting of polyethylene oxide having the formula

where n=5-50 and R and R′ are independently H, CH₃, C₂H₅, C₃H₇, or other homologs; and at least one blowing agent.
 23. The composition of claim 22, wherein said polyethylene oxide is an ethoxylated polyethylene oxide having the formula

where n=5-50.
 24. The composition of claim 22, further comprising at least one infrared attenuating agent.
 25. The composition of claim 23, wherein said one or more infrared attenuating agent is selected from nanographite, carbon black, powdered amorphous carbon, activated carbon, asphalt, granulated asphalt, milled glass, fiber glass strands, mica, black iron oxide, metal flakes, metal oxides, carbon nanotube, nanographene platelets, carbon nanofiber, activated carbon, titanium dioxide and combinations thereof.
 26. The composition of claim 22, wherein said at least blowing agent is selected from hydrofluorocarbons, C₁ to C₉ aliphatic hydrocarbons, C₁ to C₃ aliphatic alcohols, carbon dioxide, acetone, natural gases, air, water, ketones, ethers, methyl formate, hydrogen peroxide and combinations thereof.
 27. The composition of claim 22, wherein said composition is free of added polystyrene.
 28. The composition of claim 22, wherein a ration of styrene to maleic anhydride in said styrene/maleic anhydride copolymer (S:MA) ratio ranges from 70:30 (S:MA) to 99:1 (S:MA). 